1. Field of the Invention
This invention generally relates to an apparatus for testing of semiconductor laser devices, and more particularly, to an apparatus for testing of semiconductor laser devices during the manufacturing thereof and at a point in time at which the laser devices first become functional, prior to packaging of the same.
2. Discussion of the Related Art
In the manufacturing of semiconductor laser devices, the primary steps include: growing and processing double heterostructures on a substrate by, for example, liquid phase epitaxy; cleaving the processed wafer into bars containing many laser diodes (hereinafter referred to as "laser bars"); coating the two exposed cleaved facets of each laser bar with a protective coating; cleaving individual laser diode chips from the laser bars; bonding electrical leads to the chips; and packaging the chips. The laser bar is the first form at which a laser device is fully functional. The laser bar consists of a number of laser devices, from a few devices to many devices. The laser bar is usually cleaved into separate laser devices or it may be used as an array. The laser bar may further be comprised of pairs of laser devices.
Upon cleaving of the laser devices from the laser bar, packaging of the individual laser devices or diodes is one of the most expensive components of laser device production. Determination of whether or not a laser diode is functional has typically been determined or tested after the laser diode has been packaged. Therefore, packaging of a defective or non-functional laser diode is an expensive proposition, particularly in light of high volume manufacturing. It would be highly desirable to test the laser diodes or devices to determine their functionality and/or operability prior to the packaging of the same. Upon such a determination of the non-functioning of a particular laser diode, the non-functional laser diode could be identified and/or discarded prior to packaging of the same to avoid unnecessary packaging.
In Japanese Patent Application No. JP 2-266239, published Oct. 31, 1990, a semiconductor laser inspecting device is disclosed. In the inspecting device, a solid-state image pickup element is used for inspecting light beams from plural light emitting points of a chip to be measured. Probes are used for injecting current into the light emitting elements of the chip. An integral intensity of image pickup patterns are obtained and a arithmetic operation is performed. Thereafter, a prescribed operating current and an oscillation threshold current can be obtained for the chip. The JP 2-266239 device suffers, however, in that it is not well suited for high volume testing in a high volume manufacturing environment. More particularly, the JP 2-266239 device provides no suitable alignment of individual laser bars with respect to the probes nor with respect to the detector, for volume testing purposes. Alignment errors associated with manual loading can lead to unwanted reflections, which further introduces errors and leads to faulty and/or complicated measurements. Contamination problems can also arise with the JP 2-266239 device in that dirt and/or debris can accumulate undesirably between the guiding surface of the test platform and the devices under test, such an area not subject to being easily cleaned. The JP 2-266239 device further suffers from an inability to test multiple characteristics of the devices under test. Still further, the JP 2-266239 device is inadequate for minimizing a handling of the devices under test, thereby subjecting such devices under test to increased probability of being damaged and further adversely affecting testing yield. The JP 2-266239 device is not well suited nor is it easily adaptable for use as a high throughput, high yield device.
In U.S. Pat. No. 4,489,477, a device for screening laser diodes, and in particular, for multiple die burn in, is disclosed. The '477 device includes a row of probes for contacting with and feeding current though to the devices under test. The '477 device suffers from alignment, loading and handling problems which are similar to those as discussed above with respect to the JP 2-266239 device and further in conjunction with high volume testing. For instance, the devices under test of the '477 device rest upon a gold plated heatsink and are not securely held in place, thus alignment of the devices, probes, and detector with respect to one another is not highly repeatable, as is necessary and required for high volume testing. The '477 device is further not well suited for performing a multiciplicity of tests upon the devices under test. The '477 device is not suitable nor is it easily adaptable for use as a high throughput, high yield testing device.
It would thus be desirable to provide an apparatus for testing laser devices in a form at which they first become functional, thereby determining the functionality thereof and to facilitate and substantially eliminate unnecessary packaging of non-functional devices. It is further highly desirable to minimize detrimental handling, thus reducing probability for damage and contamination, of laser bars during a testing thereof. Providing an ability for performing a multiciplicity of tests upon each laser device, while minimizing a handling thereof, is further highly desirable.